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arXiv cs/0502047cs.LO
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线性序上一阶逻辑的简洁性

The succinctness of first-order logic on linear orders

Martin Grohe, Nicole Schweikardt

摘要:

简洁性是比较不同逻辑的强度的一种自然的衡量标准。直观地说,如果所有可以在L_2中表示的性质都可以在L_1中用(大约)相同大小的公式表示,但某些性质可以在L_1中用(明显)更小的公式表示,则逻辑L_1比另一逻辑L_2更简洁。我们研究线性序上逻辑的简洁性。我们的第一个定理是关于一阶逻辑的有限变量片断的。证明了:(1)在多项式因子下,一阶逻辑的2-和3-变量片段在线性序上具有相同的简洁性。(ii)4变量片段比3变量片段以指数方式更简洁。我们的第二个主要结果比较了线性序上的一阶逻辑与一元二阶逻辑的简洁性。我们证明了一元二阶逻辑的片段在线性序上具有与一阶逻辑相同的表达性,但非初等地比一阶逻辑更简洁。

英文摘要:

Succinctness is a natural measure for comparing the strength of different logics. Intuitively, a logic L_1 is more succinct than another logic L_2 if all properties that can be expressed in L_2 can be expressed in L_1 by formulas of (approximately) the same size, but some properties can be expressed in L_1 by (significantly) smaller formulas. We study the succinctness of logics on linear orders. Our first theorem is concerned with the finite variable fragments of first-order logic. We prove that: (i) Up to a polynomial factor, the 2- and the 3-variable fragments of first-order logic on linear orders have the same succinctness. (ii) The 4-variable fragment is exponentially more succinct than the 3-variable fragment. Our second main result compares the succinctness of first-order logic on linear orders with that of monadic second-order logic. We prove that the fragment of monadic second-order logic that has the same expressiveness as first-order logic on linear orders is non-elementarily more succinct than first-order logic.

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